java - HashMap get an element and set into customized value type -

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i have problem while set element , set customized value type. here customized type class user

public class user {   private list<integer> friendlist=new arraylist<integer>(); //uid list  private hashmap<string,string> checkinmap =new hashmap<string, string>(); // location , time  private int uid;   public user(int uid){     this.uid=uid;  }  public int getid(){     return uid;  }  public void setcheckins(hashmap<string,string> inmap){     this.checkinmap=(hashmap<string, string>) inmap;  }  public void setafriend(int uid){    this.friendlist.add(uid);  }   }

then, parse json array data, sure parsing json fine here.

hashmap<integer,user> usermap =new hashmap(); hashmap<string,string> inmap =new hashmap();      for(i=0;i<users.size();i++){               jsonobject auser=(jsonobject)users.get(i);               temp_uid=integer.parseint(auser.get("uid").tostring());               usermap.put(temp_uid, new user(temp_uid));               jsonarray checkins=(jsonarray)auser.get("check-ins");               for(j=0;j<checkins.size();j++){                   inmap.put( ((arraylist) checkins.get(j)).get(0).tostring(),  ((arraylist) checkins.get(j)).get(1).tostring());                }               usermap.get(i).setcheckin(inmap);               checkin_cnt=checkin_cnt+checkins.size();      }

my eclipse told me exception java.lang.nullpointerexceptionis @ line. usermap.get(i).setcheckin(inmap);

can initialize uid , set friendlist , checkinmap later? sounds wired. please give me hints or suggestions. thanks

from code should assume auser's uid same it's index.

if assumption wrong, reason, should ask usermap.get(temp_uid) not usermap.get(i)


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